Referring to FIGS. 1 and 2, an existing rotatable hanging device includes a connection seat 13, a mounting rod 11 upstanding from the connection seat 13, a first support arm 12 pivotally disposed on the connection seat 13 and spaced apart from the mounting rod 11, and a second support arm 14 rotatably extending from the first support arm 12 and having an end for mounting a display 15. Because the first support arm 12 stops rotating when abutting against the mounting rod 11, the first support arm 12 is rotatable within a relatively large angle relative to the connection seat 13. Further, since the second support arm 14 is movable along with and rotatable relative to the first support arm 12, the display 15 at the end of the second support arm 14 has a much larger rotation angle compared to that of the first support arm 12. However, in practice, the position of the display 15 need not change much, and the display 15 does not require a relatively large space for the movement thereof. Further, a wide movement range is unsuitable for installing the display 15 in a small space, on a single wall, or at a corner because the display 15 may easily be subjected to a collision force. In addition, it may be inconvenient to adjust the display 15 to an appropriate position.